Foodstuffs are subject to chemical and biological processes that can change their composition and can also produce substances harmful to health. For example, the foodstuffs may oxidize or they may be modified by enzymes and microorganisms, e.g. mold fungi. These processes must be prevented or at least delayed within the desired storage life so that foodstuffs can be safely consumed by the consumer, transported and kept stable as long as possible.
One possibility is that foodstuffs are strongly sugared, salted or dried to remove water from the foodstuff, thereby preventing the development of microorganisms, such as mold fungi or bacteria. The addition of alcohol or vinegar, the addition of preservatives and also cooling decelerate the development of microorganisms and reduce enzyme activity. Furthermore, a heat treatment can ensure that microorganisms are killed and harmful enzymes are inactivated. During pasteurization the foodstuff is heated to a temperature below 100° C. for some time. In this process, however, the comparatively resistant bacterial spores continue to be viable, and there is the risk that important nutrients and flavors are destroyed by the heat treatment.
A further method for prolonging the stability of foodstuffs consists in filling the foodstuffs into a gastight packaging and to evacuate the packaging before closing or sealing. Optionally, a protective gas or protective-gas mixtures, e.g. with nitrogen or CO2, may be added to the packaging. The activity of enzymes or microorganisms is slowed down by the displacement of air, e.g. of oxygen.
A method that has so far hardly been used—at least on an industrial scale—is the high-pressure treatment of foodstuffs. In this method a foodstuff that is normally already packaged is subjected to very high pressures of typically 400 MPa to 600 MPa for some time, for example for a few minutes. These high pressures ensure that harmful microorganisms are destroyed and killed in the foodstuff. By contrast, small molecules, e.g. vitamins, which define flavor and nutritional value of the foodstuff, are hardly altered by the high-pressure treatment. In meat products the stability can thus be prolonged for instance by the factor 6 to 10 as compared with the untreated product.
The high-pressure treatment offers various advantages over a heat treatment. For instance, the flavor is hardly changed and the vitamin content in the foodstuff is sometimes more than twice as high after a high-pressure treatment than after a heat treatment. Some heat-sensitive products, e.g. seafood, do not at all permit a heat treatment. Pathogenic germs, such as listeriae, can be killed off in a reliable way, so that the food safety is enhanced. With the high-pressure treatment, however, the internal structure of the foodstuffs can also be varied in a targeted way, resulting in novel product options, e.g. by gelling fruit preparations without any heat. Finally, the high-pressure treatment technology is already acknowledged in many countries to be (food) safe.
In the high-pressure treatment of packaged foodstuffs, problems with the packaging may arise due to the process conditions. For instance, optically disadvantageous changes and also damage may occur. Special packs with a protective-gas atmosphere pose problems due to the strongly compressible gas amount inside the package. During the high-pressure build-up and the pressure holding period, gas molecules also move into the plastic or into a film, of which the packaging of many foodstuffs is normally made. With a fast pressure reduction from e.g. 600 MPa to about 0.1 MPa ambient pressure the volume and the aggregate state, respectively, of the gas molecules changes at a faster rate than the rate at which said molecules can exit out of the film back into the interior of the packaging. The structure of the film may here get damaged. This results in optical flaws, but also in leakage within the packaging. Likewise, the product itself may get damaged due to exiting gas molecules that have passed into the product during the high-pressure treatment. This is also why vacuum packs have so far predominantly been used in high-pressure treatment.
The inactivation of microorganisms as well as the structural modification of food components are described, for example, in EP 0 588 010 A1, EP 0 689 391 B1, EP 0 752 211 B1, EP 1 100 340 B1, DE 42 26 255 A1, or DE 37 34 025 C2. EP 1 112 008 B1, EP 1 201 252 B1, DE 196 49 952 A1, DE 197 38 800 A1, DE 199 39 677 A1, and DE 26 11 389 A1 describe the effects of high-pressure treatments on microbiological storage life and the safety of food. The application of high-pressure treatment especially for meat products is described in DE 198 01 031 C2, DE 196 53 677 C1, EP 0 748 592 B1, EP 0 683 986 B1, DE 101 01 958 A1, DE 10 2005 011 868 A1, or WO 2006/097248 A1.
A generic device and a generic method are revealed in WO 2006/129180 A1. A line with two shut-off valves that are arranged one after the other is here provided for discharging the high-pressure medium out of a high-pressure container. A buffer container may additionally be disposed between the two shut-off valves for receiving the high-pressure medium. It is the objective of this system design to reduce the pressure difference on an opened discharge valve so as to prevent cavitation on the valve. During normal operation the one shut-off valve is first opened for this purpose so as to accommodate high-pressure medium in the buffer container. After the first discharge valve has been closed, the downstream second discharge valve is opened to discharge the high-pressure medium at least in part. A drawback is however that the clock cycles of this conventional high-pressure treatment system are very long—WO 2006/129180 A1 indicates a cycle time of more than one hour. Such cycle times are not profitable on an industrial scale. Moreover, neither WO 2006/129180 A1 nor the remaining prior art furnishes information as to how the high-pressure treatment could e.g. be combined with the protective gas treatment of foodstuffs.